Analyte detection is becoming increasingly important as a security and safety measure. Transportation, commercial, government, educational, and other facilities have a need for the sensitive and rapid detection of analytes, such as (but not limited to) those that are indicative of explosives or other substances that pose a threat. In addition, in industrial, residential, and commercial settings analyte detection can provide warning of particles or vapors that pose a health or safety risk. Example analytes that can be detected include hazardous materials such as but not limited to explosive-related materials, toxic industrial chemicals (TICS), or chemical or biological agents.
Analysis instruments have been developed and are under development to meet the need for detection of analytes. A non-limiting example analysis instrument currently being used in both portable and larger forms is the Ion Mobility Spectrometer (IMS). More particular examples of an IMS include the GE Vapor Tracer models, though other types of IMS may be used. Speed and sensitivity are primary concerns, and thus researchers and manufacturers seek to improve the speed and sensitivity of such analysis instruments.
A typical IMS device has separate particle and vapor modes. In a particle mode, an assembly is affixed to the device to accept and desorb particles from a substrate such as a swab (though other substrates are possible). The swab, for example, may be inserted into the assembly and heated to vaporize any collected particulates. The vapor is directed via vacuum into the instrument for analysis. Another assembly can be affixed to the device for vapor mode, a mode in which the device collects vapors for analyte detection.
Preconcentrators offer the opportunity to enhance the performance of any type of analysis instrument by increasing the concentration of analyte in a volume of fluid sent for analysis. Generally, preconcentrators collect analyte over a period of time (during adsorption) and then provide a concentrated fluid stream to the analysis instrument (during desorption).
Rapid preconcentration requires rapid heating. Accordingly, successful microscale preconcentrators have advantages regarding cycling and desorption, as heating to accomplish desorption can be conducted quickly and with low power. Example microscale preconcentrators are disclosed in U.S. Pat. No. 6,257,835 to Manginell et al., entitled “Chemical Preconcentrator with Integral Thermal Flow Sensor”, and in U.S. Pat. No. 6,171,378 to Manginell et al., entitled “Chemical Preconcentrator”. For example, a chemical preconcentrator may be formed from a substrate having a suspended membrane, such as low-stress silicon nitride. This work incorporates a flow over design.
Multiple stage designs are often used for high volume concentration. Examples of multiple stage designs are disclosed in U.S. Pat. No. 5,854,431 to Linker et al., entitled “Two Stage Preconcentrator for Vapor/Particle Detection”, and U.S. Pat. No. 6,085,601 to Linker et al., entitled “Particle Preconcentrator”.
Example microscale preconcentrators with a flow through design are disclosed in U.S. Published Patent Application No. 20050095722 (incorporated by reference herein), published May 5, 2005, and entitled “Micro scale Flow Through Sorbent Plate Collection Device”, and in U.S. Published Patent Application No. 20050226778, published Oct. 13, 2005, and entitled “Micro scale Flow Through Sorbent Plate Collection Device”. The flow through design has a number of advantages, one of which is increasing contact between analyte fluid flow and a sorbent in a collection area compared to typical flow over designs that would require creating a turbulent flow to match the level of analyte fluid-sorbent contact.
However, while one or more of the preconcentrators described above are suitable for low volume collection, high volume collection for continuous testing presents special challenges. One reason is that preconcentrators and analysis instruments have generally been designed to conduct sampling over small time periods. Accordingly, the volume of sample flow that can be accommodated is generally small.